Passive sensors, such as passive infrared sensors, have been used for the detection of humans, animals, vehicles, or other moving objects. Unlike an active sensor, a passive sensor may not normally be able to measure the range or distance between the sensor and a moving object directly. Due to the lack of range information, a passive sensor may not be able to detect the direction of motion of an object. Active sensors, such as radars or a laser detectors, may detect the direction of motion based on measured ranges and angles, but they are typically more expensive than passive sensors.